April 2005

From clues to court cases

Fire investigations dissect fire behavior and burn patterns.

Jolene Ackerman

All forest fires are investigated, regardless of the fire size or the amount of property damage. At the scene, a wildfire investigator looks for clues that indicate where the fire started: "point of origin." To find that point and cause of a fire, the investigator must know wildfire burn patterns, fire indicators and fire behavior.

Seasoned investigators use science and art to determine what started the blaze. Sometimes the cause is easily pegged – a prescribed burn that got out of control or a burn barrel. But often the evidence at the point of origin is not found intact, making the investigator's job more difficult. First responders to the scene must protect the area believed to be near the point of origin. Both the public and firefighters are kept out of this area to minimize the chance that evidence will be destroyed or washed away.

Every fire is investigated and documented as if it were going to be a court case. The fire investigators keep detailed records of observations such as license numbers of vehicles leaving the scene, tire tracks, fire behavior, and persons or aircraft in the area. An investigator's records can include written descriptions, pictures and even sketches.

Wildland fires often have common features. They usually start in light fuel such as dry grass or leaves and typically the ignition is small. Physical indicators point to the direction the fire has burned. For example, the way soot marks rocks, tree trunks and other dense or nonflammable items will show an experienced fire investigator the fire's path. Other indicators can be the way light fuels are left unburned or the way burn patterns are left on small shrubs and twigs. Combining all of the indicators points out key information to a trained investigator.

Wildfire investigators and fire control personnel are always on the lookout for potential serial arsonists. If not caught, these fire setters can get bolder with time and move from wildland fires to empty buildings and even to occupied structures. Consequently, a thorough investigation needs to be conducted on even the smallest grass fire as it may have been set by a budding arsonist.